Hello,
I signed up for SS benefits for Dec. 2021 with first check in Jan 2022. Started Medicare Nov 1,2021. Got a letter saying they are deducting past- due Medicare premiums of $764.10 from my Jan check. And the letter says we withheld $170.10 for med insurance premiums from the Jan payment. If I just started Medicare Nov 1, shouldn't just $148.50x2 be withheld for past-due, not $764.10? I'm not subjuecto IRRMA. Thank you.

Hi. Well, it certainly sounds like it based on your description. The standard monthly Part B premium amount for 2021 is $148.50, so if you aren't subject to IRMAA then you'd only owe a total of $297 for your Part B premiums for November and December.

However, if you've signed up for Parts C (i.e. Medicare Advantage) and/or D (i.e. Prescription coverage) of Medicare with a private insurance company and if you've authorized those premiums to be withheld from your Social Security benefits, then the past due amount may include those premiums. Otherwise, I don't have any explanation for you. You should be able to get an explanation by calling Social Security, though.

Best, Jerry